Hitherto, flexible polyurethane foams, with large commercial application, have been based on polyol skeletons such as polyethers and polyesters. Flexible polyurethanes made from polyethers and polyesters are inherently subject to hydrolysis because both of the resulting polyurethane foams are hydrophilic in nature. Although polyether polyurethane foams are more resistant to hydrolysis than polyester polyurethane foams, both still suffer from hydrolytic instability, and, therefore, are not usable in applications which require extended periods in contact with water such as waterproofing. These two types of flexible polyurethane foams also have low oxidative resistance and therefore, possess rather poor weathering properties.
Other flexible polyurethane foams also have been prepared using more hydrophobic flexible units such as hydroxy terminated polybutadienes and hydroxy terminated polyethylene-polypropylene copolymers. Although these flexible polyurethane foams have excellent resistance to hydrolysis, they both have poor weathering and heat resistance due either to the existence of double bonds in the case of the polybutadiene polyurethane foams, or active hydrogens, tertiary hydrogens, in the case of polyethylene-polypropylene polyurethane foams.